Semiconductor lasers used in fiber-optic transmission systems are expensive and temperamental and require special driving circuitry. Those drivers typically use feedback from one or more monitored quantities to ensure optimum performance.
Dallas Semiconductor's DS1859 chip monitors and controls the laser driver bias and modulation currents. It targets the manufacturers of small form-factor (SFF) or SFF-pluggable (SFP) optical modules. Also, it's SFF-8472-compatible for multisource-agreement (MSA) optical transceivers.
The DS1859's two 50-kÙ, 256-position linear variable resistors are digitally settable for controlling laser bias and modulation currents. These dual temperature-controlled nonvolatile variable resistors have settings that can be changed every 2°C. Values stored in on-chip EEPROM lookup tables control the resistor value.
The chip measures temperature, supply voltage, and three other analog inputs (MON1, MON2, and MON3) that typically will be feedback signals from the laser driver (such as transmitted power, received power, and transmitter bias). A built-in 12-bit analog-to-digital converter provides conversion for the analog inputs for digital processing.
The built-in temperature sensor provides a direct digital output. A two-wire serial port supplies an interface to an external microcontroller that offers the calculations for calibration. Alarm and warning flags are provided.
The DS1859 comes in 16-pin TSSOP and 4- by 4-mm BGA packages. It operates from a 2.7- to 5.5-V supply. Pricing starts at $3.92 for lots of 1000 and up. An evaluation kit is also available.
Dallas Semiconductor (Maxim-IC)